A resistor R, a capacitor C and an inductor L, which are used as passive devices in an electronic circuit, may have their respective typical functions and roles but may be combined together, to perform a new circuit function. For example, a capacitor basically interrupts a direct current and allows an alternating current signal to pass but it may form a time constant circuit, a time delay circuit, an RC filter and an LC filter. Further, a capacitor itself may remove a noise. An inductor removes a high frequency noise and performs a function of impedance matching and the like.
Due to its resistance being varied according to an applied voltage, a varistor is widely used as a protection device of protecting important electronic devices and circuits against an over-voltage (a surge voltage) and static electricity. That is, when an over-voltage is applied in both ends of a varistor by the over-voltage or a bolt of lightning, the resistance of the varistor rapidly decreases so that no current flows into another device and the circuit is protected against the over-voltage.
As electronic machines become smaller in size, varistors are developed to be small and arrayed, to protect a chip device for a highly-integrated circuit against static electricity and over-voltages. Further, a varistor may be combined with another device, to perform composite functions. When a varistor is combined with a resistor, an important electronic device or circuit can be efficiently protected against over-voltages. When a varistor is combined with an inductor, noise can be removed, thereby stably securing operation of the electronic device or circuit.
When no over-voltage is applied, a resistor-varistor combination device performs a function of a resistor-capacitor combination device. Further, when no over-voltage is applied, a combination of an inductor and a varistor can realize a nor L-type filter formed of an inductor and a capacitor with an excellent characteristic of removing a high frequency noise.
When an abnormal over-voltage flows into a circuit, the aforementioned resistor-varistor combination device or inductor-varistor combination device immediately realizes the function of the varistor to interrupt the over-voltage as described above. In general, proper combinations of the three typical passive devices, i.e., the resistor, inductor and capacitor, can perform the functions of matching impedance and removing high frequency-low frequency noises or selecting signals of a specific frequency band.
To realize the composite functions, the above-described combination device is connected by a wire and the like after each component is separately mounted onto a printed circuit board and the like. However, since mounting an individual device increases an area for the mounting, it does not meet the requirements for diverse small application machines.
Accordingly, a single device with the composite functions needs to be realized. However, a composite device using a single material is limited in performing various functions. For example, a resistor-capacitor (varistor) filter has been presented as a composite component including the function of an LC filter and the function of the varistor to control ESD. However, this filter has the problems of signals generated by a resistance element, power loss and a complicate manufacturing process.
On the other hand, there is a demand for an inductor-capacitor (varistor) composite component not only to control the ESD but also to remove a noise in broader frequency band. An example of the aforementioned composite component may be realized by combining an inductor of low inductance being below 100 nH and a varistor by the application of a single dielectric material. However, in this case, the noise can be removed only in a high frequency band.
A composite component of a high inductance inductor (below 5 μH) and a varistor can be considered by using a magnetic material and a dielectric material. However, when the magnetic material and the dielectric material are joined together and thermally treated at a high temperature, since interdiffusion is generated between the different materials during a firing process, the composite component has the problems in that electrical characteristics and durability of the final device deteriorate.
Moreover, when multilayered different materials undergo co-firing process, it is difficult to match firing shrinkage between the different materials. Thus, compared to the manufacturing of each component using a single material, it is very difficult to control the conditions of a manufacturing process of the composite device.
Consequently, when a single composite device is manufactured by forming the different materials to be integrally with each other, there are many problems in that it is difficult to secure stabilized characteristics of the device, a yield is not good and a manufacturing cost increases. Therefore, there are many problems to be solved with respect to the reliability of the device and the productivity thereof.
Therefore, the present invention is directed to provide a composite electronic device being made of different materials.
Another object of the present invention is to provide a single composite device with excellent electrical and mechanical characteristics.
Another object of the present invention is to provide a composite device which performs the function of a varistor while provides excellent characteristics of removing a noise in broad frequency band.
The other objects and features of the present invention will be presented in more detail below:
In accordance with an aspect of the present invention, the present invention provides a magnetic and dielectric composite electronic device comprising: a first region where a plurality of magnetic material sheets are layered; a second region where a plurality of dielectric material sheets are layered; and a third region as a middle layer interposed between the first region and the second region, including a Zn—Ti-based material to prevent diffusion of the materials when the first region and the second region undergo co-firing process, and the first region, the second region and the third region are integrally formed in a single body.
The third region may be formed of a single sheet or a composite sheet with a plurality of sheets being layered, and it may include powder of, preferably, ZnO of 0.5˜1.0 mol and TiO2 of 0.5˜1.0 mol. The third region may further include Bi2O3 of 0.1˜0.35 mol, and it may further include NiO being or less than 0.1 mol and/or MnCO3 being or less than 0.1 mol.
The electronic device may be formed in a single chip type by forming one electrode pattern on each of the sheets of the first region formed of the magnetic material and each of the sheets of the second region, or it may be formed in an array-type chip (barrage chip) by forming a plurality of electrode patterns on each of the sheets of the first region formed of the magnetic material and each of the sheets of the second region.
The composite electronic device according to the present invention may be represented by an equivalent circuit in which a varistor and a capacitor are positioned towards an input terminal of the device at one side of one inductor, and another varistor and another capacitor are positioned towards an output terminal of the device at the other side of the inductor, and each varistor and each capacitor are grounded. Further, the composite electronic device may be represented by an equivalent circuit in which one varistor and one capacitor are positioned at one side of one inductor towards either an input terminal or an output terminal of the device, and the varistor and the capacitor are grounded.
In the present invention, the Zn—Ti-based material of the third region may be formed on the whole sheet or it may be formed on parts of the sheet so that the rest may be formed of a dielectric material or a magnetic material.
In accordance with the present invention, there is provided the multilayered chip-type electronic device being compounded of the inductor and the varistor. A function of electromagnetic interference (EMI) is performed and an effect of controlling electrostatic discharge (ESD) is obtained by realizing a low pass filter having a function of the varistor. Furthermore, in accordance with the present invention, the one-chip electronic device, which has the composite functions of the LC filter and the varistor of protecting the ESD, is manufactured by a simple process, and the durability and electrical characteristics of a product is secured by preventing the interdiffusion between the different materials respectively forming the magnetic and the dielectric parts.